Recordable optical recording media have been developed since 1980s. Said media mainly comprise a substrate, a recording layer, a reflective layer and a protective layer. At present, the organic materials suitable for the recording layer of recordable optical recording media, such as compact disks (often referred to as CD-R) comprise cyanine dyes, phthalocyanine dyes and azo dyes and the likes. These dyes commonly have a maximal absorption at a wavelength of 650 nm to 750 nm in the visible light range. As a major function, the dyes absorb a laser beam of 780 nm and then convert it into thermal energy, such that the recording layer changes in its optical characteristics to fulfill the reflectance requirements as set forth in the specification of the compact disks (Red Book). In view thereof, organic materials having a major light absorption at a wavelength outside the wavelength range of the laser beam are needed for the recording layer of the optical recording media.
Therefore, since 1990s, in order to satisfy the trend of continuous data expansion, all the major CD manufacturers make efforts at the improvements of the recording density of the CDs. To that end, the spaces between the pits and between the tracks are decreased and, in the meantime, the laser beams for reading signal are narrowed to avoid the signal cross-talk between the tracks and to raise the discriminated ratio of track length. As a result, almost all the current developments are concentrated on the laser beams with wavelengths of 635 nm to 660 nm.
According to the current developmental trend of the optical recording media, organic materials for the recordable optical recording media used at laser beams with 650 nm preferably has a light absorption at a wavelength of from 540 nm to 600 nm.
In general, one of the common materials for recording layers in the application of optical recording media is a cyanine dye. However, owing to the poor light resistance and the storage difficulty of said cyanine dye, metal chelate compounds of azo dyes having superior light- and weather resistance are suitable for recording layer. For example, U.S. Pat. No. 5,532,342 discloses an azo metal chelate compound formed from a sulfonylphenyl-based azo compound and a variety of metal ligands, which may be applied to optical recording media, whereby a recording layer having an absorption wavelength of from 700 nm to 730 nm may be prepared.